In a conventional display apparatus such as a TV set, CRT (Cathode Ray Tube) has prevailed. Recently, however, the performances such as viewing angle, contrast, color reproducibility has been improved apart from space saving and power saving features. A liquid crystal display apparatus of matrix type is successor to the CRTs.
The liquid crystal display apparatus of matrix type has a display area provided with a plurality of scanning signal lines, a plurality of data signal lines that are provided so as to be perpendicular to and to intersect with the scanning signal lines, TFTs (Thin Film Transistors) as control switches each provided at each intersection of the scanning signal lines and the data signal lines. The liquid crystal display apparatus is further provided with (a) a scanning signal line driving circuit (gate driver) for outputting the scanning signals to the scanning signal lines, (b) a data signal line driving circuit (data driver) for outputting to the data signal lines the display signals corresponding to display data, and (c) a control circuit (controller) for controlling the scanning signal line driving circuit and the data signal line driving circuit, respectively. With the arrangement, the display signal is applied to a pixel electrode connected to the TFT that has been selected in response to the scanning signal, so as to control the alignment of the liquid crystal pixels in response to the difference of voltages between the pixel electrode and the opposed electrode.
The liquid crystal is capacitive load. On this account, when a display signal voltage is applied to the pixel electrode, the liquid crystal has the holding property in which the alignment, varying depending on the display signal voltage thus applied, is held. Because of this property, unlike the CRT, it is possible to obtain a display screen without flickering, unlike the CRT. On the other hand, the response speed of the liquid crystal itself, especially the response to halftone is not enough in one frame period of image input signal, thereby arising the problem that the residual image is found in the moving image.
Further, in the liquid crystal display apparatus, the display signal, which has been written into a corresponding pixel, keeps to be held during a time period in which the TFT is not selected. On this account, even if the response speed of the liquid crystal is made fast, the residual image exists on the retina. This is because human being follows one's eyes to the moving image. Thus, another problem arises that the display quality deteriorates.
In view of the circumstances, the following liquid crystal method is proposed in the Japanese unexamined patent publication No. 11-109921 (publication date: Apr. 23, 1999) which corresponds to U.S. Pat. No. (USP 6,396,469 B1), so as to solve the foregoing problems.
According to the arrangement disclosed in the publication, a screen is divided into upper and lower screens (a) such that the signal scanning for the upper screen and a black signal (blanking) scanning for the lower screen are simultaneously carried out during the first half of one frame period, and (b) such that the signal scanning for the lower screen and a black signal (blanking) scanning for the upper screen are simultaneously carried out during the second half of the one frame period.
With the arrangement, when focusing attention on a specific pixel, it is inevitable that both image display period and black display period exist in one frame period. Especially, the existence of the black display period ensures that the image can be displayed without mixing the prior and subsequent frame data. It is possible to improve the display performance of moving image, accordingly.
The conventional arrangement, however, results in that the black display is always carried out on either one of the upper and lower screens in one frame period, thereby causing that the entire brightness of the display screen is lowered.